Inertia free drive for cryogenic piston expander

ABSTRACT

A cryogenic piston expander may reduce or eliminate the inertia of system, as compared to conventional cryogenic piston expanders that utilize a heavy flywheel. The cryogenic piston expander of the present invention may use a single bent running from a motor to a large sprocket mounted on a main shaft of the cryogenic piston expander.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority of U.S. provisional patent application No. 61/366,622, filed Jul. 22, 2010, the contents of which are herein incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to cryogenic piston expanders and, more particularly, to an inertia free drive for a cryogenic piston expander.

Systems operating at cryogenic temperatures generally have a cryogenic refrigeration unit attached to the system to minimize or eliminate boil-off of the cryogenic coolant. A cryogenic refrigeration unit including an expansion device, compressor, and heat exchanger is known. High pressure fluid from the compressor is passed through the heat exchanger and introduced into the expansion device, such as a cryogenic piston expander. Expansion of the fluid in the expansion device reduces the temperature and pressure of the fluid. Heat energy is transferred from the expanding fluid by the performance of mechanical work.

Conventional cryogenic piston expanders require a large amount of inertia, typically due to the rotation of a large flywheel. This flywheel may be up to about 200 pounds in weight. This large amount of inertia may increase the load on the variable frequency drive (VFD) motor, cause belt dusting and may require frequent maintenance.

Referring to FIG. 1, a conventional cryogenic piston expander 12 may include a large flywheel 14. A motor 16 may turn a driving pulley 18, turning a belt 20 attached to a driven pulley 22 of a jack shaft 24. A jack shaft driving pulley 23 may turn a second belt 26 to turn the flywheel 14. Due to the weight of the flywheel 14, the motor 16 may have a large load applied thereto.

As can be seen, there is a need for cryogenic piston expander that may function without the need for a large flywheel.

SUMMARY OF THE INVENTION

In one aspect of the present invention, a cryogenic piston expander comprises a motor adapted to drive a motor shaft; a first sprocket attached to the motor shaft; a second sprocket attached to a main shaft of the cryogenic piston expander; and a belt connecting the first sprocket to the second sprocket, wherein the first sprocket is smaller than the second sprocket.

In another aspect of the present invention, a cryogenic piston expander, comprises a variable frequency drive motor adapted to drive a motor shaft; a first sprocket attached to the motor shaft; a second sprocket attached to a main shaft of the cryogenic piston expander; and a belt connecting the first sprocket to the second sprocket, wherein the cryogenic piston expander operates without a flywheel.

These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a cryogenic piston expander according to the prior art; and

FIG. 2 is a side view of a cryogenic piston expander according to an exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description is of the best currently contemplated modes of carrying out exemplary embodiments of the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims.

Various inventive features are described below that can each be used independently of one another or in combination with other features.

Broadly, an embodiment of the present invention provides a cryogenic piston expander may reduce or eliminate the inertia of the system, as compared to conventional cryogenic piston expanders. The cryogenic piston expander of the present invention may use a single bent running from a motor to a large sprocket mounted on a main shaft of the cryogenic piston expander.

Referring to FIG. 2, a cryogenic piston expander 10 may include a motor 32 mounted off a base plate 36 of the cryogenic piston expander 10. In some embodiments, the motor 32 may be mounted at about a 2:00 position relative to the main shaft 38 of the cryogenic piston expander 10.

A smaller sprocket 34 may be attached to a motor shaft 40. A larger sprocket 30 may be attached to the main shaft 38 of the cryogenic piston expander 10. A belt 28 may transfer rotation of the smaller sprocket 34 into rotation of the larger sprocket 30.

The motor 32 may be a variable frequency drive (VFD) motor. The motor 32 may provide control of the rotational speed of the main shaft 38. A VFD inverter (not shown) may control the speed of the motor 32. Due to the ratio of the smaller sprocket 34 to the larger sprocket 30, the rotation of the motor shaft 40 may be slower than if the sprockets 34, 30 were more similar in size. In some embodiments, the larger sprocket 30 may have a diameter that is from about 2 times to about 10 times, typically from about 5 times to about 7 times, the diameter of the smaller sprocket 34.

The cryogenic piston expander 10 may use less space on the base plate as compared to the conventional cryogenic piston expander 12 as shown in FIG. 1. There is no need for a flywheel or a jack shaft in the cryogenic piston expander 10 of the present invention.

The cryogenic piston expander 10 may be used on piston expanders working on helium cryogenic machines.

It should be understood, of course, that the foregoing relates to exemplary embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims. 

1. A cryogenic piston expander comprising: a motor adapted to drive a motor shaft; a first sprocket attached to the motor shaft; a second sprocket attached to a main shaft of the cryogenic piston expander; and a belt connecting the first sprocket to the second sprocket, wherein the first sprocket is smaller than the second sprocket.
 2. The cryogenic piston expander of claim 1, wherein the cryogenic piston expander operates without a flywheel.
 3. The cryogenic piston expander of claim 1, wherein the cryogenic piston expander operates without a jack shaft.
 4. The cryogenic piston expander of claim 1, wherein the belt directly connects the first sprocket to the second sprocket.
 5. A cryogenic piston expander, comprising: a first sprocket attached to a motor shaft; a second sprocket attached to a main shaft of the cryogenic piston expander; and a belt connecting the first sprocket to the second sprocket, wherein the cryogenic piston expander operates without a flywheel.
 6. The cryogenic piston expander of claim 5, wherein the cryogenic piston expander operates without a jack shaft.
 7. The cryogenic piston expander of claim 5, wherein the belt directly connects the first sprocket to the second sprocket. 